Implant encapsulation

ABSTRACT

An implant unit may include a substrate and an implantable circuit arranged on the substrate. An encapsulation structure may be disposed over at least a portion of the substrate and at least a portion of the implantable circuit, the encapsulation structure including a parylene layer and a silicon layer disposed over the parylene layer.

RELATED APPLICATIONS

The present application is a divisional of application Ser. No.13/952,063, filed on Jul. 26, 2013, issued as U.S. Pat. No. 8,838,256 onSep. 16, 2014, which claims the benefit of U.S. Provisional PatentApplication No. 61/676,327, filed on Jul. 26, 2012, the entiredisclosures of which are hereby incorporated by reference.

BACKGROUND

Neural modulation presents the opportunity to treat many physiologicalconditions and disorders by interacting with the body's own naturalneural processes. Neural modulation includes inhibition (e.g. blockage),stimulation, modification, regulation, or therapeutic alteration ofactivity, electrical or chemical, in the central, peripheral, orautonomic nervous system. By modulating the activity of the nervoussystem, for example through the stimulation of nerves or the blockage ofnerve signals, several different goals may be achieved. Motor neuronsmay be stimulated at appropriate times to cause muscle contractions.Sensory neurons may be blocked, for instance to relieve pain, orstimulated, for instance to provide a signal to a subject. In otherexamples, modulation of the autonomic nervous system may be used toadjust various involuntary physiological parameters, such as heart rateand blood pressure.

Among the conditions to which neural modulation may be applied isobstructive sleep apnea (OSA). OSA is a respiratory disordercharacterized by recurrent episodes of partial or complete obstructionof the upper airway during sleep. During the sleep of a person with OSA,the pharyngeal muscles relax during sleep and gradually collapse,narrowing the airway. The airway narrowing limits the effectiveness ofthe sleeper's breathing, causing a rise in CO₂ levels in the blood. Theincrease in CO₂ results in the pharyngeal muscles contracting to openthe airway to restore proper breathing. The largest of the pharyngealmuscles responsible for upper airway dilation is the genioglossusmuscle, which is one of several different muscles in the tongue. Thegenioglossus muscle is responsible for forward tongue movement and thestiffening of the anterior pharyngeal wall. In patients with OSA, theneuromuscular activity of the genioglossus muscle is decreased comparedto normal individuals, accounting for insufficient response andcontraction to open the airway as compared to a normal individual. Thislack of response contributes to a partial or total airway obstruction,which significantly limits the effectiveness of the sleeper's breathing.In OSA patients, there are often several airway obstruction eventsduring the night. Because of the obstruction, there is a gradualdecrease of oxygen levels in the blood (hypoxemia). Hypoxemia leads tonight time arousals, which may be registered by EEG, showing that thebrain awakes from any stage of sleep to a short arousal. During thearousal, there is a conscious breath or gasp, which resolves the airwayobstruction. An increase in sympathetic tone activity rate through therelease of hormones such as epinephrine and noradrenaline also oftenoccurs as a response to hypoxemia. As a result of the increase insympathetic tone, the heart enlarges in an attempt to pump more bloodand increase the blood pressure and heart rate, further arousing thepatient. After the resolution of the apnea event, as the patient returnsto sleep, the airway collapses again, leading to further arousals.

These repeated arousals, combined with repeated hypoxemia, leaves thepatient sleep deprived, which leads to daytime somnolence and worsenscognitive function. This cycle can repeat itself up to hundreds of timesper night in severe patients. Thus, the repeated fluctuations in andsympathetic tone and episodes of elevated blood pressure during thenight evolve to high blood pressure through the entire day.Subsequently, high blood pressure and increased heart rate may causeother diseases.

Efforts for treating OSA include Continuous Positive Airway Pressure(CPAP) treatment, which requires the patient to wear a mask throughwhich air is blown into the nostrils to keep the airway open. Othertreatment options include the implantation of rigid inserts in the softpalate to provide structural support, tracheotomies, or tissue ablation.

Another condition to which neural modulation may be applied is theoccurrence of migraine headaches. Pain sensation in the head istransmitted to the brain via the occipital nerve, specifically thegreater occipital nerve, and the trigeminal nerve. When a subjectexperiences head pain, such as during a migraine headache, theinhibition of these nerves may serve to decrease or eliminate thesensation of pain.

Neural modulation may also be applied to hypertension. Blood pressure inthe body is controlled via multiple feedback mechanisms. For example,baroreceptors in the carotid body in the carotid artery are sensitive toblood pressure changes within the carotid artery. The baroreceptorsgenerate signals that are conducted to the brain via theglossopharyngeal nerve when blood pressure rises, signaling the brain toactivate the body's regulation system to lower blood pressure, e.g.through changes to heart rate, and vasodilation/vasoconstriction.Conversely, parasympathetic nerve fibers on and around the renalarteries generate signals that are carried to the kidneys to initiateactions, such as salt retention and the release of angiotensin, whichraise blood pressure. Modulating these nerves may provide the ability toexert some external control over blood pressure.

The foregoing are just a few examples of conditions to whichneuromodulation may be of benefit, however embodiments of the inventiondescribed hereafter are not necessarily limited to treating only theabove-described conditions.

SUMMARY

Some embodiments of the present disclosure include an implant unitconfigured to provide protection to the implant unit various components.

In some embodiments, the implant unit may include a substrate; animplantable circuit arranged on the substrate; and an encapsulationstructure disposed over at least a portion of the substrate and at leasta portion of the implantable circuit. The encapsulation structure mayinclude a first polymer layer having a first density; and a secondpolymer layer disposed over the first polymer layer and having a densitywhich is less than the first density.

Another embodiment of the disclosure may include a method forencapsulating an implant unit. The method may include providing asubstrate, the substrate including an implantable circuit disposedthereon; and covering at least a portion of the substrate and at least aportion of the implantable circuit with an encapsulation structure,wherein the step of covering includes: disposing a first polymer layerover at least a portion of the substrate and at least a portion of theimplantable circuit; and disposing a second polymer layer over the firstpolymer layer, wherein the second polymer layer has a density less thanthe first polymer layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of thedisclosure and, together with the description, serve to explain theprinciples of the embodiments disclosed herein.

FIG. 1 schematically illustrates an implant unit and external unit,according to an exemplary embodiment of the present disclosure.

FIG. 2 is a partially cross-sectioned side view of a subject with animplant unit and external unit, according to an exemplary embodiment ofthe present disclosure.

FIG. 3 schematically illustrates a system including an implant unit andan external unit, according to an exemplary embodiment of the presentdisclosure.

FIG. 4 is a top view of an exemplary implant unit according to someembodiments.

FIG. 5 is a top view of an alternate embodiment of an implant unit,according to an exemplary embodiment of the present disclosure.

FIG. 6 illustrates circuitry of an implant unit and an external unit,according to an exemplary embodiment of the present disclosure.

FIG. 7 illustrates a graph of quantities that may be used in determiningenergy delivery as a function coupling, according to an exemplarydisclosed embodiment.

FIG. 8 depicts a graph illustrating non-linear harmonics.

FIG. 9 depicts a graph of quantities that may be used in determiningenergy delivery as a function coupling, according to an exemplarydisclosed embodiment.

FIG. 10 illustrates additional features of an exemplary embodiment ofimplant unit 110.

FIGS. 11 a and 11 b illustrate a double-layer crossover antenna.

FIG. 12 a provides a diagrammatic side sectional view of the implantunit encapsulation, according to an exemplary disclosed embodiment.

FIG. 12 b illustrates a first and second window of exposure of theimplant unit encapsulation, according to an exemplary disclosedembodiment.

FIG. 12 c provides another diagrammatic side sectional view of theimplant unit encapsulation, according to an exemplary disclosedembodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Although the present disclosure is being initially described in thecontext of treatment of OSA through modulating nerve, the presentmedical device may be employed in any patient/portion of a body wherenerve modulation may be desired. That is, in addition to use in patientswith migraine headaches, or hypertension, embodiments of the presentdisclosure may be used in many other areas, including, but not limitedto: deep brain stimulation (e.g., treatment of epilepsy, Parkinson's,and depression); cardiac pace-making, stomach muscle stimulation (e.g.,treatment of obesity), back pain, incontinence, menstrual pain, and/orany other condition that may be affected by neural modulation.

Embodiments of the present disclosure relate generally to a device formodulating a nerve through the delivery of energy. Nerve modulation maytake the form of nerve stimulation, which may include providing energyto the nerve to create a voltage change sufficient for the nerve toactivate, or propagate an electrical signal of its own. Nerve modulationmay also take the form of nerve inhibition, which may include providingenergy to the nerve sufficient to prevent the nerve from propagatingelectrical signals. Nerve inhibition may be performed through theconstant application of energy, and may also be performed through theapplication of enough energy to inhibit the function of the nerve forsome time after the application. Other forms of neural modulation maymodify the function of a nerve, causing a heightened or lessened degreeof sensitivity. As referred to herein, modulation of a nerve may includemodulation of an entire nerve and/or modulation of a portion of a nerve.For example, modulation of a motor neuron may be performed to affectonly those portions of the neuron that are distal of the location towhich energy is applied.

In patients with OSA, for example, a primary target response of nervestimulation may include contraction of a tongue muscle (e.g., themuscle) in order to move the tongue to a position that does not blockthe patient's airway. In the treatment of migraine headaches, nerveinhibition may be used to reduce or eliminate the sensation of pain. Inthe treatment of hypertension, neural modulation may be used toincrease, decrease, eliminate or otherwise modify nerve signalsgenerated by the body to regulate blood pressure.

FIG. 1 illustrates an implant unit and external unit, according to anexemplary embodiment of the present disclosure. An implant unit 110, maybe configured for implantation in a subject, in a location that permitsit to modulate a nerve 115. The implant unit 110 may be located in asubject such that intervening tissue 111 exists between the implant unit110 and the nerve 115. Intervening tissue may include muscle tissue,connective tissue, organ tissue, or any other type of biological tissue.Thus, location of implant unit 110 does not require contact with nerve115 for effective neuromodulation. The implant unit 110 may also belocated directly adjacent to nerve 115, such that no intervening tissue111 exists.

In treating OSA, implant unit 110 may be located on a genioglossusmuscle of a patient. Such a location is suitable for modulation of thehypoglossal nerve, branches of which run inside the genioglossus muscle.Implant unit 110 may also be configured for placement in otherlocations. For example, migraine treatment may require subcutaneousimplantation in the back of the neck, near the hairline of a subject, orbehind the ear of a subject, to modulate the greater occipital nerveand/or the trigeminal nerve. Treating hypertension may require theimplantation of a neuromodulation implant intravascularly inside therenal artery or renal vein (to modulate the parasympathetic renalnerves), either unilaterally or bilaterally, inside the carotid arteryor jugular vein (to modulate the glossopharyngeal nerve through thecarotid baroreceptors). Alternatively or additionally, treatinghypertension may require the implantation of a neuromodulation implantsubcutaneously, behind the ear or in the neck, for example, to directlymodulate the glossopharyngeal nerve.

External unit 120 may be configured for location external to a patient,either directly contacting, or close to the skin 112 of the patient.External unit 120 may be configured to be affixed to the patient, forexample, by adhering to the skin 112 of the patient, or through a bandor other device configured to hold external unit 120 in place. Adherenceto the skin of external unit 120 may occur such that it is in thevicinity of the location of implant unit 110.

FIG. 2 illustrates an exemplary embodiment of a neuromodulation systemfor delivering energy in a patient 100 with OSA. The system may includean external unit 120 that may be configured for location external to thepatient. As illustrated in FIG. 2, external unit 120 may be configuredto be affixed to the patient 100. FIG. 2 illustrates that in a patient100 with OSA, the external unit 120 may be configured for placementunderneath the patient's chin and/or on the front of patient's neck. Thesuitability of placement locations may be determined by communicationbetween external unit 120 and implant unit 110, discussed in greaterdetail below. In alternate embodiments, for the treatment of conditionsother than OSA, the external unit may be configured to be affixedanywhere suitable on a patient, such as the back of a patient's neck,i.e. for communication with a migraine treatment implant unit, on theouter portion of a patient's abdomen, i.e. for communication with astomach modulating implant unit, on a patient's back, i.e. forcommunication with a renal artery modulating implant unit, and/or on anyother suitable external location on a patient's skin, depending on therequirements of a particular application.

External unit 120 may further be configured to be affixed to analternative location proximate to the patient. For example, in oneembodiment, the external unit may be configured to fixedly or removablyadhere to a strap or a band that may be configured to wrap around a partof a patient's body. Alternatively, or in addition, the external unitmay be configured to remain in a desired location external to thepatient's body without adhering to that location.

The external unit 120 may include a housing. The housing may include anysuitable container configured for retaining components. In addition,while the external unit is illustrated schematically in FIG. 2, thehousing may be any suitable size and/or shape and may be rigid orflexible. Non-limiting examples of housings for the external unit 100include one or more of patches, buttons, or other receptacles havingvarying shapes and dimensions and constructed of any suitable material.In one embodiment, for example, the housing may include a flexiblematerial such that the external unit may be configured to conform to adesired location. For example, as illustrated in FIG. 2, the externalunit may include a skin patch, which, in turn, may include a flexiblesubstrate. The material of the flexible substrate of the external unitmay include, but is not limited to, plastic, silicone, woven naturalfibers, and other suitable polymers, copolymers, and combinationsthereof. Any portion of external unit 120 may be flexible or rigid,depending on the requirements of a particular application.

As previously discussed, in some embodiments external unit 120 may beconfigured to adhere to a desired location. Accordingly, in someembodiments, at least one side of the housing may include an adhesivematerial. The adhesive material may include a biocompatible material andmay allow for a patient to adhere the external unit to the desiredlocation and remove the external unit upon completion of use. Theadhesive may be configured for single or multiple uses of the externalunit. Suitable adhesive materials may include, but are not limited tobiocompatible glues, starches, elastomers, thermoplastics, andemulsions.

FIG. 3 schematically illustrates a system including external unit 120and an implant unit 110. In some embodiments, internal unit 110 may beconfigured as a unit to be implanted into the body of a patient, andexternal unit 120 may be configured to send signals to and/or receivesignals from implant unit 110.

As shown in FIG. 3, various components may be included within a housingof external unit 120 or otherwise associated with external unit 120. Asillustrated in FIG. 3, at least one processor 144 may be associated withexternal unit 120. For example, the at least one processor 144 may belocated within the housing of external unit 120. In alternativeembodiments, the at least one processor may be configured for wired orwireless communication with the external unit from a location externalto the housing.

The at least one processor may include any electric circuit that may beconfigured to perform a logic operation on at least one input variable.The at least one processor may therefore include one or more integratedcircuits, microchips, microcontrollers, and microprocessors, which maybe all or part of a central processing unit (CPU), a digital signalprocessor (DSP), a field programmable gate array (FPGA), or any othercircuit known to those skilled in the art that may be suitable forexecuting instructions or performing logic operations.

FIG. 3 illustrates that the external unit 120 may further be associatedwith a power source 140. The power source may be removably couplable tothe external unit at an exterior location relative to external unit.Alternatively, as shown in FIG. 3, power source 140 may be permanentlyor removably coupled to a location within external unit 120. The powersource may further include any suitable source of power configured to bein electrical communication with the processor. In one embodiment, forexample the power source 140 may include a battery.

The power source may be configured to power various components withinthe external unit. As illustrated in FIG. 3, power source 140 may beconfigured to provide power to the processor 144. In addition, the powersource 140 may be configured to provide power to a signal source 142.The signal source 142 may be in communication with the processor 144 andmay include any device configured to generate a signal (e.g., asinusoidal signal, square wave, triangle wave, microwave,radio-frequency (RF) signal, or any other type of electromagneticsignal). Signal source 142 may include, but is not limited to, awaveform generator that may be configured to generate alternatingcurrent (AC) signals and/or direct current (DC) signals. In oneembodiment, for example, signal source 142 may be configured to generatean AC signal for transmission to one or more other components. Signalsource 142 may be configured to generate a signal of any suitablefrequency. In some embodiments, signal source 142 may be configured togenerate a signal having a frequency of from about 6.5 MHz to about 13.6MHz. In additional embodiments, signal source 142 may be configured togenerate a signal having a frequency of from about 7.4 to about 8.8 MHz.In further embodiments, signal source 142 may generate a signal having afrequency as low as 90 kHz or as high as 28 MHz.

Signal source 142 may be configured for direct or indirect electricalcommunication with an amplifier 146. The amplifier may include anysuitable device configured to amplify one or more signals generated fromsignal source 142. Amplifier 146 may include one or more of varioustypes of amplification devices, including, for example, transistor baseddevices, operational amplifiers, RF amplifiers, power amplifiers, or anyother type of device that can increase the gain associated one or moreaspects of a signal. The amplifier may further be configured to outputthe amplified signals to one or more components within external unit120.

The external unit may additionally include a primary antenna 150. Theprimary antenna may be configured as part of a circuit within externalunit 120 and may be coupled either directly or indirectly to variouscomponents in external unit 120. For example, as shown in FIG. 3,primary antenna 150 may be configured for communication with theamplifier 146.

The primary antenna may include any conductive structure that may beconfigured to create an electromagnetic field. The primary antenna mayfurther be of any suitable size, shape, and/or configuration. The size,shape, and/or configuration may be determined by the size of thepatient, the placement location of the implant unit, the size and/orshape of the implant unit, the amount of energy required to modulate anerve, a location of a nerve to be modulated, the type of receivingelectronics present on the implant unit, etc. The primary antenna mayinclude any suitable antenna known to those skilled in the art that maybe configured to send and/or receive signals. Suitable antennas mayinclude, but are not limited to, a long-wire antenna, a patch antenna, ahelical antenna, etc. In one embodiment, for example, as illustrated inFIG. 3, primary antenna 150 may include a coil antenna. Such a coilantenna may be made from any suitable conductive material and may beconfigured to include any suitable arrangement of conductive coils(e.g., diameter, number of coils, layout of coils, etc.). A coil antennasuitable for use as primary antenna 150 may have a diameter of betweenabout 1 cm and 10 cm, and may be circular or oval shaped. In someembodiments, a coil antenna may have a diameter between 5 cm and 7 cm,and may be oval shaped. A coil antenna suitable for use as primaryantenna 150 may have any number of windings, e.g. 4, 8, 12, or more. Acoil antenna suitable for use as primary antenna 150 may have a wirediameter between about 0.01 mm and 2 mm. These antenna parameters areexemplary only, and may be adjusted above or below the ranges given toachieve suitable results.

As noted, implant unit 110 may be configured to be implanted in apatient's body (e.g., beneath the patient's skin). FIG. 2 illustratesthat the implant unit 110 may be configured to be implanted formodulation of a nerve associated with a muscle of the subject's tongue130. Modulating a nerve associated with a muscle of the subject's tongue130 may include stimulation to cause a muscle contraction. In furtherembodiments, the implant unit may be configured to be placed inconjunction with any nerve that one may desire to modulate. For example,modulation of the occipital nerve, the greater occipital nerve, and/orthe trigeminal nerve may be useful for treating pain sensation in thehead, such as that from migraines. Modulation of parasympathetic nervefibers on and around the renal arteries (i.e. the renal nerves), thevagus nerve, and/or the glossopharyngeal nerve may be useful fortreating hypertension. Additionally, any nerve of the peripheral nervoussystem (both spinal and cranial), including motor neurons, sensoryneurons, sympathetic neurons and parasympathetic neurons, may bemodulated to achieve a desired effect.

Implant unit 110 may be formed of any materials suitable forimplantation into the body of a patient. In some embodiments, implantunit 110 may include a substrate such as, for example, flexible carrier161 (FIG. 4) including a flexible, biocompatible material. Suchmaterials may include, for example, silicone, polyimides,phenyltrimethoxysilane (PTMS), polymethyl methacrylate (PMMA), ParyleneC, polyimide, liquid polyimide, laminated polyimide, black epoxy,polyether ether ketone (PEEK), Liquid Crystal Polymer (LCP), Kapton,etc. Implant unit 110 and flexible carrier 161 may also be fabricatedwith a thickness suitable for implantation under a patient's skin.Implant 110 may have thickness of less than about 4 mm or less thanabout 2 mm. The term “flexible” as used herein may refer to a capabilityof changing a component physical shape while maintaining its desiredfunctionality. For example, a component may be considered flexible if itcan bend or flex or stretch, etc. allowing the component to conform totissue (e.g., muscle, adipose, bone, connective, etc.) in a subject'sbody.

Implant unit 110 may further include an implantable circuit arranged onthe substrate. The implantable circuit 180 may be in electricalcommunication (e.g., either directly or indirectly connected) with atleast a pair of modulation electrodes and/or an antenna on thesubstrate. The implantable circuit and/or modulation electrodes mayinclude conductive materials, such as gold, platinum, titanium, or anyother biocompatible conductive material or combination of materials. Insome embodiments, the implantable circuit may include one or moremeandering electrical traces 1060 (FIG. 10) configured to maintainelectrical contact during flexing. The implantable circuit may variouscomponents such as diodes, capacitors, resistors, etc.

Other components that may be included in or otherwise associated withthe implant unit are illustrated in FIG. 3. For example, implant unit110 may include a secondary antenna 152 mounted onto or integrated withflexible carrier 161. Similar to the primary antenna, the secondaryantenna may include any suitable antenna known to those skilled in theart that may be configured to send and/or receive signals. The secondaryantenna may include any suitable size, shape, and/or configuration. Thesize, shape and/or configuration may be determined by the size of thepatient, the placement location of the implant unit, the amount ofenergy required to modulate the nerve, etc. Suitable antennas mayinclude, but are not limited to, a long-wire antenna, a patch antenna, ahelical antenna, etc. In some embodiments, for example, secondaryantenna 152 may include a coil antenna having a circular shape (see alsoFIG. 4) or oval shape. Such a coil antenna may be made from any suitableconductive material and may be configured to include any suitablearrangement of conductive coils (e.g., diameter, number of coils, layoutof coils, etc.). A coil antenna suitable for use as secondary antenna152 may have a diameter of between about 5 mm and 30 mm, and may becircular or oval shaped. A coil antenna suitable for use as secondaryantenna 152 may have any number of windings, e.g., 4, 15, 20, 30, or 50.A coil antenna suitable for use as secondary antenna 152 may have a wirediameter between about 0.001 mm and 1 mm. These antenna parameters areexemplary only, and may be adjusted above or below the ranges given toachieve suitable results.

FIGS. 11 a and 11 b illustrate a double-layer crossover antenna 1101suitable for use as either primary antenna 150 or secondary antenna 152.While a double-layer crossover antenna is shown and described, otherantenna configurations may be suitable for primary antenna 150 and/orsecondary antenna 152. For example, single layer antennas may be usedwhere antenna components (e.g., coils) are arranged in a single layer,e.g., either on or within a dielectric or insulating material. Also,while a crossover pattern is shown, other patterns may also be suitable.For example, in some embodiments, a wire associated with primary antenna150 and/or secondary antenna 152 may include a pattern of traces ofprogressively decreasing dimension. In the case of traces arranged incoils, for example, each loop could include rings of progressivelydecreasing diameter to create a pattern that spirals inwardly. A similarapproach may be viable using traces of other shapes as well.

Returning to FIG. 11 a, this figure illustrates a single coil ofdouble-layer crossover antenna 1101, while FIG. 11 b illustrates twolayers of double layer crossover antenna 1101. Antenna 1101 may includea first coil of wire 1102 arranged on a first side of a dielectriccarrier 1104 and a second coil of wire 1103 on a second side of adielectric carrier 1104.

Arranging the antenna coils in a double layer may serve to increase thetransmission range of the antenna without increasing the size of theantenna. Such an arrangement, however, may also serve to increasecapacitance between the wires of each coil. In each wire coil, an amountof parasitic capacitance between wires may partially depend on thedistance each wire is from its neighbor. In a single layer coil,capacitance may be generated between each loop of the coil and itsneighbors to either side. Thus, more compact coils may generate moreparasitic capacitance. When a second layer coil is added, additionalcapacitance may then be generated between the wires of the first coiland the wires of the second coil. This additional capacitance may befurther increased if corresponding loops of the first and second coilshave the same or similar diameters, and/or if a dielectric carrierseparating the loops is made very thin. Increased parasitic capacitancein an antenna may serve to alter characteristics, such as resonantfrequency, of the antenna in unpredictable amounts based onmanufacturing specifications. Additionally, resonant frequency drift,caused, for example by moisture incursion or antenna flexing, may beincreased by the presence of increased parasitic capacitance. Thus, inorder to decrease variability in the manufactured product, it may beadvantageous to reduce the levels of parasitic capacitance in a duallayer antenna.

FIG. 11 b illustrates a double layer crossover antenna 1101 which mayserve to reduce the parasitic capacitance in a manufactured antenna. Asillustrated in FIG. 11 b, a first coil of wire 1102 is concentricallyoffset from a second coil of wire 1103. In contrast to a configurationwhere each loop of a first coil 1102 has the same diameter ascorresponding loop of the second coil 1103, concentrically offsettingcorresponding loops of each wire coil serves to increase the distancebetween a single loop of the first coil 1102 with a corresponding loopof the second coil 1103. This increased distance, in turn, may decreasethe parasitic wire-to-wire capacitance between loops of first coil 1102and corresponding loops of second coil 1103. This configuration may beparticularly advantageous in reducing parasitic capacitance in asituation where a dielectric carrier 1104 is thin enough such that theconcentric distance by which each coil is offset is relatively largecompared to the thickness of the dielectric carrier 1104. For example,in a situation where a dielectric carrier is 0.5 mm thick, a concentricoffset of 0.5 mm or more may produce a large change in parasiticcapacitance. In contrast, in a situation where a dielectric carrier is 5mm thick, a concentric offset of 0.5 mm may produce a smaller change inparasitic capacitance. The concentric offset between a first coil 1102and a second coil 1103 may be achieved, for example, by a plurality ofelectrical trace steps 1105 that offset each loop of the coils from eachpreceding loop. Electrical trace steps 1105 on a first side ofdielectric carrier 1104 cross over electrical trace steps 1105 on asecond side of dielectric carrier 1104, thus providing the crossoverfeature of double-layer crossover antenna 1101.

In additional embodiments, double layer crossover antenna 1101 mayinclude openings 1106 in dielectric carrier 1104 to facilitate theelectrical connection of first and second coils 1102, 1103. First andsecond coils 1102, 1103 of double layer crossover antenna 1101 may alsoinclude exposed electrical portions 1108 configured to electricallyconnect with a connector of a device housing that may be coupled toantenna 1101. Exposed electrical portions 1108 may be configured so asto maintain electrical contact with the connector of a device housingindependent of the axial orientation of the connection. As shown in FIG.11 a, for example, exposed electrical portions 1108 may be configured ascontinuous or discontinuous circles in order to achieve this. A firstexposed electrical portion 1108 configured as a discontinuous circle mayprovide a space through which an electrical trace may pass withoutcontacting the first exposed electrical portion, for example to connectwith a second exposed electrical portion located inside the first, or toother components located within the circle of the first exposedelectrical portion 1108. FIG. 11 a illustrates an antenna havingsubstantially elliptical coils; other shapes, such as circular,triangular, square, etc., may be also be used in different embodiments.Elliptical coils may facilitate placement of external unit 120 incertain areas (e.g., under the chin of a subject) while maintainingdesirable electrical performance characteristics.

Implant unit 110 may additionally include a plurality offield-generating implant electrodes 158 a, 158 b. The electrodes mayinclude any suitable shape and/or orientation on the implant unit solong as the electrodes may be configured to generate an electric fieldin the body of a patient. Implant electrodes 158 a and 158 b may alsoinclude any suitable conductive material (e.g., copper, silver, gold,platinum, iridium, platinum-iridium, platinum-gold, conductive polymers,etc.) or combinations of conductive (and/or noble metals) materials. Insome embodiments, for example, the electrodes may include short lineelectrodes, circular electrodes, and/or circular pairs of electrodes. Asshown in FIG. 4, electrodes 158 a and 158 b may be located on an end ofa first extension 162 a of an elongate arm 162. The electrodes, however,may be located on any portion of implant unit 110. Additionally, implantunit 110 may include electrodes located at a plurality of locations, forexample on an end of both a first extension 162 a and a second extension162 b of elongate arm 162, as illustrated, for example, in FIG. 5.Implant electrodes may have a thickness between about 200 nanometers and1 millimeter. Anode and cathode electrode pairs may be spaced apart byabout a distance of about 0.2 mm to 25 mm. In additional embodiments,anode and cathode electrode pairs may be spaced apart by a distance ofabout 1 mm to 10 mm, or between 4 mm and 7 mm. Adjacent anodes oradjacent cathodes may be spaced apart by distances as small as 0.001 mmor less, or as great as 25 mm or more. In some embodiments, adjacentanodes or adjacent cathodes may be spaced apart by a distance betweenabout 0.2 mm and 1 mm.

FIG. 4 provides a schematic representation of an exemplary configurationof implant unit 110. As illustrated in FIG. 4, in one embodiment, thefield-generating electrodes 158 a and 158 b may include two sets of fourcircular electrodes, provided on flexible carrier 161, with one set ofelectrodes providing an anode and the other set of electrodes providinga cathode. Implant unit 110 may include one or more structural elementsto facilitate implantation of implant unit 110 into the body of apatient. Such elements may include, for example, elongated arms, sutureholes, polymeric surgical mesh, biological glue, spikes of flexiblecarrier protruding to anchor to the tissue, spikes of additionalbiocompatible material for the same purpose, etc. that facilitatealignment of implant unit 110 in a desired orientation within apatient's body and provide attachment points for securing implant unit110 within a body. For example, in some embodiments, implant unit 110may include an elongate arm 162 having a first extension 162 a and,optionally, a second extension 162 b. Extensions 162 a and 162 b may aidin orienting implant unit 110 with respect to a particular muscle (e.g.,the genioglossus muscle), a nerve within a patient's body, or a surfacewithin a body above a nerve. For example, first and second extensions162 a, 162 b may be configured to enable the implant unit to conform atleast partially around soft or hard tissue (e.g., nerve, bone, ormuscle, etc.) beneath a patient's skin. Further, implant unit 110 mayalso include one or more suture holes 160 located anywhere on flexiblecarrier 161. For example, in some embodiments, suture holes 160 may beplaced on second extension 162 b of elongate arm 162 and/or on firstextension 162 a of elongate arm 162. Implant unit 110 may be constructedin various shapes. Additionally, or alternatively, implant unit 110 mayinclude surgical mesh or other perforatable material, e.g., withinsuture holes 1050, described in greater detail below with respect toFIG. 10. In some embodiments, implant unit may appear substantially asillustrated in FIG. 4. In other embodiments, implant unit 110 may lackillustrated structures such as second extension 162 b, or may haveadditional or different structures in different orientations.Additionally, implant unit 110 may be formed with a generallytriangular, circular, or rectangular shape, as an alternative to thewinged shape shown in FIG. 4. In some embodiments, the shape of implantunit 110 (e.g., as shown in FIG. 4) may facilitate orientation ofimplant unit 110 with respect to a particular nerve to be modulated.Thus, other regular or irregular shapes may be adopted in order tofacilitate implantation in differing parts of the body.

FIG. 5 is a perspective view of an alternate embodiment of an implantunit 110, according to an exemplary embodiment of the presentdisclosure. As illustrated in FIG. 5, implant unit 110 may include aplurality of electrodes, located, for example, at the ends of firstextension 162 a and second extension 162 b. FIG. 5 illustrates anembodiment wherein implant electrodes 158 a and 158 b include short lineelectrodes.

As illustrated in FIG. 4, secondary antenna 152 and electrodes 158 a,158 b may be mounted on or integrated with flexible carrier 161. Variouscircuit components and connecting wires may be used to connect secondaryantenna with implant electrodes 158 a and 158 b. To protect the antenna,electrodes, and implantable circuit components from the environmentwithin a patient's body, implant unit 110 may include a protectivecoating that encapsulates implant unit 110. In some embodiments, theprotective coating may be made from a flexible material to enablebending along with flexible carrier 161. The encapsulation material ofthe protective coating may also resist humidity penetration and protectagainst corrosion. In some embodiments, the protective coating mayinclude a plurality of layers, including different materials orcombinations of materials in different layers.

In some embodiments of the present disclosure, the encapsulationstructure of implanted unit may include two layers. For example, a firstlayer may be disposed over at least a portion of the implantable circuitarranged on the substrate, and a second layer may be disposed over thefirst layer. In some embodiments, the first layer may be disposeddirectly over the implantable circuit, but in other embodiments, thefirst layer may be disposed over an intervening material between thefirst layer and the implantable circuit. In some embodiments, the firstlayer may provide a moisture barrier and the second layer may provide amechanical protection (e.g., at least some protection from physicaldamage that may be caused by scratching, impacts, bending, etc.) for theimplant unit. The terms “encapsulation” and “encapsulate” as used hereinmay refer to complete or partial covering of a component. In someembodiments component may refer to a substrate, implantable circuit,antenna, electrodes, any parts thereof, etc. The term “layer” as usedherein may refer to a thickness of material covering a surface orforming an overlying part or segment. The layer thickness can bedifferent from layer to layer and may depend on the covering materialand the method of forming the layer. For example, a layer disposed bychemical vapor may be thinner than a layer disposed through othermethods.

Other configurations may also be employed. For example, another moisturebarrier may be formed over the outer mechanical protection layer. Insuch embodiments, a first moisture barrier layer (e.g., parylene) may bedisposed over (e.g., directly over or with intervening layers) theimplantable circuit, a mechanical protection layer (e.g., silicone) maybe formed over the first moisture barrier, and second moisture barrier(e.g., parylene) may be disposed over the mechanical protection layer.

FIG. 10 illustrates exemplary embodiment of encapsulated implant unit110. Exemplary embodiments may incorporate some or all of the featuresillustrated in FIG. 10 as well as additional features. A protectivecoating of implant unit 110 may include a primary capsule 1021. Primarycapsule 1021 may encapsulate the implant unit 110 and may providemechanical protection for the implant unit 110. For example, thecomponents of implant unit 110 may be delicate, and the need to handlethe implant unit 110 prior to implantation may require additionalprotection for the components of implant unit 110, and primary capsule1021 may provide such protection. Primary capsule 1021 may encapsulateall or some of the components of implant unit 110. For example, primarycapsule 1021 may encapsulate antenna 152, flexible carrier 161, andimplantable circuit 180. The primary capsule may leave part or all ofelectrodes 158 a, 158 b exposed enabling them to deliver energy formodulating a nerve unimpeded by material of the primary capsule. Inalternative embodiments, different combinations of components may beencapsulated or exposed.

Primary capsule 1021 may be fashioned of a material and thickness suchthat implant unit 110 remains flexible after encapsulation. Primarycapsule 1021 may include any suitable bio-compatible material, such assilicone, or polyimides, phenyltrimethoxysilane (PTMS), polymethylmethacrylate (PMMA), Parylene C, liquid polyimide, laminated polyimide,polyimide, Kapton, black epoxy, polyether ketone (PEEK), Liquid CrystalPolymer (LCP), or any other suitable biocompatible coating.

FIG. 12 a is a diagrammatic sectional view showing an encapsulatedimplant unit 110 according to an exemplary disclosed embodiment. Theprotective coating of implant unit 110 may include primary capsule 1021along with a secondary capsule 1070. In some embodiments, primarycapsule 1021 may be formed of a polymer material having a density lessthan a density of a polymer material used to form secondary capsule1070. For example, in some embodiments, primary capsule 1021 may includesilicone, polyurethane, epoxy, acrylic, etc., and secondary capsule 1070may include parylene N, parylene C, parylene HD, parylene D, etc.Additionally, other embodiments may include an outer barrier 1022 (FIG.12 c) formed over the primary capsule 1021. The outer barrier 1022 mayserve as a moisture barrier or may be selected to provide other desiredproperties. For example, in some embodiments the outer barrier 1022 maybe formed of a polymer having a density greater than the density of theprimary capsule 1021. The outer barrier 1022 may be formed of parylene,for example.

Secondary capsule 1070 may provide environmental protection for theimplant unit 110 when it is implanted in the body. For example, primarycapsule 1021 may be constructed of silicone, which may be subject tomoisture incursion from the body. Such moisture incursion may limit alife-span of the implant unit 110 due to possible corrosive effects.Secondary capsule 1070 may be provided underneath the primary capsule1021 to protect implant unit 110 from the corrosive effects of bodilyimplantation. For example, a layer of parylene may serve as a secondarycapsule and may be provided to encapsulate all or some of the componentsof implant unit 110.

In exemplary embodiments, secondary capsule 1070 may encapsulate any orall components associated with implant unit 110 and may fully orpartially cover those components. For example, secondary capsule 1070may cover the substrate, secondary antenna 152, carrier 161, implantablecircuit 180, and electrodes 158 a, 158 b. The secondary capsule 1070may, in turn, be encapsulated by primary capsule 1021.

In some embodiments, secondary capsule 1070 may cover less than all ofthe components of implant unit 110. For example, in some embodiments, atleast a portion of electrode 158 a and/or 158 b may remain uncovered bysecondary capsule 1070. Similarly, as noted above, portions of electrode158 a and/or 158 b may remain uncovered by primary capsule 1021. In someembodiments, as illustrated in FIG. 12 b, a secondary window of exposure1081 through secondary capsule 1070 may be smaller than a primary windowof exposure 1082 through primary capsule 1021. Thus, from a perspectiveabove electrode 158 a, for example, an exposed lip of materialassociated with secondary capsule 1070 the edge of which forms thesecondary window of exposure 1081 through secondary capsule 1070 wouldextend beyond a boundary of the primary window of exposure 1082 throughprimary capsule 1021.

Secondary capsule 1070, may include, for example parylene, parylene C orany other suitable material for preventing the effects of moistureincursion on implant unit 110. In some embodiments, a secondary capsulelayer 1070 may be deposited by chemical vapor deposition and may have athickness of about 1 molecule in thickness, between 1 and 5 molecules inthickness, or any other suitable film thickness.

Some combinations of primary and secondary capsule materials, such assilicone and parylene C, may bond relatively weakly to one another.Where such combinations of materials are used, a plurality perforationsor penetrating holes 1030 (FIG. 12 a) may be provided to pass throughboth carrier 161 and a secondary capsule 1070 to improve the adherenceof the primary capsule 1021 to implant unit 110. For example, whenpenetrating holes 1030 are provided, the material of primary capsule1021 may flow through the penetrating holes during fabrication,permitting the material of primary capsule 1021 to flow into and adhereto itself. A plurality of penetrating holes 1030 provided throughcarrier 161 and a secondary capsule 1070 may provide anchor points topermit the self-adherence of the material used to form primary capsule1021. Penetrating holes 1030 may be provided and sized such that, afterencapsulation by primary capsule 1021, at least some portion of holes1030 remain free of primary capsule material, or they may be providedand sized such that, after encapsulation, holes 1030 are filled in (asillustrated in FIG. 12 a).

Also illustrated in FIG. 10 are suture holes 1050,1062, and 1064, whichmay include a mesh material 1065, such as a surgical mesh disposedtherein. The surgical mesh may provide a larger target area for surgeonsto use when suturing implant unit 110 into place during implantation.The entire surgical mesh may be encapsulated by primary capsule 1021,permitting a surgeon to pass a needle through any portion of the meshwithout compromising the integrity of implant unit 110. Surgical meshmay additionally be used to cover one or more suture holes 1050,permitting larger suture holes 1050 that may provide surgeons with agreater target area. Surgical mesh may also encourage surrounding tissueto bond with implant unit 110. In some embodiments, a surgeon may pass asurgical suture needle through suture holes 1062, 1064 located on oneextension 162 a of an elongate arm 162 of implant unit 110, throughtissue of the subject, and through surgical mesh provided on a secondextension 162 b of elongate arm 162 of implant unit 110. In thisembodiment, the larger target area provided by suture holes 1050 mayfacilitate the suturing process because it may be more difficult toprecisely locate a suture needle after passing it through tissue.Implantation and suturing procedures may be further facilitated throughthe use of a delivery tool, described in greater detail below.

The capsules of implant unit 110 may be provided such that implant unit110 remains flexible after encapsulation. Additionally, implant unit 110may include meandering electrical traces 1060 in order to maintainelectrical contact under flexural conditions. As used herein, meanderingelectrical traces 1060 may include any electrical trace that is longerthan the shortest distance between the points that it connects.Meandering electrical traces 1060 may also include any trace ofsufficient length so as to maintain electrical conductivity duringflexing of a carrier on which it is located. For example, as shown inFIG. 10, meandering electrical traces 1060 may be configured as lineshaving successive curves, such as waves or the like. Repeated flexing ofcarrier 161 on which electrical traces are deposited may causedegradation of the electrical traces, as they are repeatedly stressedwith the flexure of carrier 161. Meandering electrical traces 1060 mayprovide an increased lifetime, as the additional slack provided mayserve to reduce stress in the traces during flexing of carrier 161.Meandering electrical traces 1060 may include any suitable conductivematerial, such as gold, platinum, titanium, copper, silver, iridium,platinum-iridium, platinum-gold, conductive polymers, any conductivebiocompatible material, and/or combinations of conductive (and/or noblemetals) materials.

In additional embodiments consistent with the present disclosure,conductive electrical elements of implant unit 110, such as meanderingtraces 1060 and electrodes 158 a, 158 b may be provided through aprogressive metallization layering method. In some embodiments, flexiblecarrier 161 may include a material, such as liquid crystal polymer, thatbonds relatively weakly to conductive metals desirable for use asconductive electrical elements, such as titanium and/or gold. Aprogressive metallization layering method may utilize a temporarybonding layer, including a metal, such as nickel, that may bond morestrongly to flexible carrier 161. The temporary bonding layer may belayered with the metals desirable for use as conductive electricalelements and used to provide an initial bond with the material offlexible carrier 161. The temporary bonding layer may then be removedthrough dissolution, erosion, or similar technique, through flexiblecarrier 161, leaving the desirable metals in place in flexible carrier161.

In one embodiment, a progressive metallization layering method may beutilized to provide gold and titanium conductive elements on a liquidcrystal polymer carrier 161. The conductive elements may be constructedfrom progressive layers of nickel, gold, and titanium. Next, liquidcrystal polymer may be molded around the conductive elements, bondingstrongly with the nickel layer and forming a recess containing thelayered conductive element. Finally, the nickel may be removed throughthe liquid crystal polymer through dissolution, erosion, or similartechnique. The removal of nickel leaves the gold/titanium layeredconductive element in place, held tightly in the liquid crystal polymerrecess created during the molding process.

Returning to FIGS. 2 and 3, external unit 120 may be configured tocommunicate with implant unit 110. For example, in some embodiments, aprimary signal may be generated on primary antenna 150, using, e.g.,processor 144, signal source 142, and amplifier 146. More specifically,in one embodiment, power source 140 may be configured to provide powerto one or both of the processor 144 and the signal source 142. Theprocessor 144 may be configured to cause signal source 142 to generate asignal (e.g., an RF energy signal). Signal source 142 may be configuredto output the generated signal to amplifier 146, which may amplify thesignal generated by signal source 142. The amount of amplification and,therefore, the amplitude of the signal may be controlled, for example,by processor 144. The amount of gain or amplification that processor 144causes amplifier 146 to apply to the signal may depend on a variety offactors, including, but not limited to, the shape, size, and/orconfiguration of primary antenna 150, the size of the patient, thelocation of implant unit 110 in the patient, the shape, size, and/orconfiguration of secondary antenna 152, a degree of coupling betweenprimary antenna 150 and secondary antenna 152 (discussed further below),a desired magnitude of electric field to be generated by implantelectrodes 158 a, 158 b, etc. Amplifier 146 may output the amplifiedsignal to primary antenna 150.

External unit 120 may communicate a primary signal on primary antenna tothe secondary antenna 152 of implant unit 110. This communication mayresult from coupling between primary antenna 150 and secondary antenna152. Such coupling of the primary antenna and the secondary antenna mayinclude any interaction between the primary antenna and the secondaryantenna that causes a signal on the secondary antenna in response to asignal applied to the primary antenna. In some embodiments, couplingbetween the primary and secondary antennas may include capacitivecoupling, inductive coupling, radiofrequency coupling, etc. and anycombinations thereof.

Coupling between primary antenna 150 and secondary antenna 152 maydepend on the proximity of the primary antenna relative to the secondaryantenna. That is, in some embodiments, an efficiency or degree ofcoupling between primary antenna 150 and secondary antenna 152 maydepend on the proximity of the primary antenna to the secondary antenna.The proximity of the primary and secondary antennas may be expressed interms of a coaxial offset (e.g., a distance between the primary andsecondary antennas when central axes of the primary and secondaryantennas are co-aligned), a lateral offset (e.g., a distance between acentral axis of the primary antenna and a central axis of the secondaryantenna), and/or an angular offset (e.g., an angular difference betweenthe central axes of the primary and secondary antennas). In someembodiments, a theoretical maximum efficiency of coupling may existbetween primary antenna 150 and secondary antenna 152 when both thecoaxial offset, the lateral offset, and the angular offset are zero.Increasing any of the coaxial offset, the lateral offset, and theangular offset may have the effect of reducing the efficiency or degreeof coupling between primary antenna 150 and secondary antenna 152.

As a result of coupling between primary antenna 150 and secondaryantenna 152, a secondary signal may arise on secondary antenna 152 whenthe primary signal is present on the primary antenna 150. Such couplingmay include inductive/magnetic coupling, RF coupling/transmission,capacitive coupling, or any other mechanism where a secondary signal maybe generated on secondary antenna 152 in response to a primary signalgenerated on primary antenna 150. Coupling may refer to any interactionbetween the primary and secondary antennas. In addition to the couplingbetween primary antenna 150 and secondary antenna 152, circuitcomponents associated with implant unit 110 may also affect thesecondary signal on secondary antenna 152. Thus, the secondary signal onsecondary antenna 152 may refer to any and all signals and signalcomponents present on secondary antenna 152 regardless of the source.

While the presence of a primary signal on primary antenna 150 may causeor induce a secondary signal on secondary antenna 152, the couplingbetween the two antennas may also lead to a coupled signal or signalcomponents on the primary antenna 150 as a result of the secondarysignal present on secondary antenna 152. A signal on primary antenna 150induced by a secondary signal on secondary antenna 152 may be referredto as a primary coupled signal component. The primary signal may referto any and all signals or signal components present on primary antenna150, regardless of source, and the primary coupled signal component mayrefer to any signal or signal component arising on the primary antennaas a result of coupling with signals present on secondary antenna 152.Thus, in some embodiments, the primary coupled signal component maycontribute to the primary signal on primary antenna 150.

Implant unit 110 may be configured to respond to external unit 120. Forexample, in some embodiments, a primary signal generated on primary coil150 may cause a secondary signal on secondary antenna 152, which inturn, may cause one or more responses by implant unit 110. In someembodiments, the response of implant unit 110 may include the generationof an electric field between implant electrodes 158 a and 158 b.

FIG. 6 illustrates circuitry 170 that may be included in external unit120 and circuitry 180 that may be included in implant unit 110.Additional, different, or fewer circuit components may be included ineither or both of circuitry 170 and circuitry 180. As shown in FIG. 6,secondary antenna 152 may be arranged in electrical communication withimplant electrodes 158 a, 158 b. In some embodiments, circuitryconnecting secondary antenna 152 with implant electrodes 158 a and 158 bmay cause a voltage potential across implant electrodes 158 a and 158 bin the presence of a secondary signal on secondary antenna 152. Thisvoltage potential may be referred to as a field inducing signal, as thisvoltage potential may generate an electric field between implantelectrodes 158 a and 158 b. More broadly, the field inducing signal mayinclude any signal (e.g., voltage potential) applied to electrodesassociated with the implant unit that may result in an electric fieldbeing generated between the electrodes.

The field inducing signal may be generated as a result of conditioningof the secondary signal by circuitry 180. As shown in FIG. 6, circuitry170 of external unit 120 may be configured to generate an AC primarysignal on primary antenna 150 that may cause an AC secondary signal onsecondary antenna 152. In certain embodiments, however, it may beadvantageous (e.g., in order to generate a unidirectional electric fieldfor modulation of a nerve) to provide a DC field inducing signal atimplant electrodes 158 a and 158 b. To convert the AC secondary signalon secondary antenna 152 to a DC field inducing signal, circuitry 180 inimplant unit 110 may include an AC-DC converter. The AC to DC convertermay include any suitable converter known to those skilled in the art.For example, in some embodiments the AC-DC converter may includerectification circuit components including, for example, diode 156 andappropriate capacitors and resistors. In alternative embodiments,implant unit 110 may include an AC-AC converter, or no converter, inorder to provide an AC field inducing signal at implant electrodes 158 aand 158 b.

As noted above, the field inducing signal may be configured to generatean electric field between implant electrodes 158 a and 158 b. In someinstances, the magnitude and/or duration of the generated electric fieldresulting from the field inducing signal may be sufficient to modulateone or more nerves in the vicinity of electrodes 158 a and 158 b. Insuch cases, the field inducing signal may be referred to as a modulationsignal. In other instances, the magnitude and/or duration of the fieldinducing signal may generate an electric field that does not result innerve modulation. In such cases, the field inducing signal may bereferred to as a sub-modulation signal.

Various types of field inducing signals may constitute modulationsignals. For example, in some embodiments, a modulation signal mayinclude a moderate amplitude and moderate duration, while in otherembodiments, a modulation signal may include a higher amplitude and ashorter duration. Various amplitudes and/or durations of field-inducingsignals across electrodes 158 a, 158 b may result in modulation signals,and whether a field-inducing signal rises to the level of a modulationsignal can depend on many factors (e.g., distance from a particularnerve to be stimulated; whether the nerve is branched; orientation ofthe induced electric field with respect to the nerve; type of tissuepresent between the electrodes and the nerve; etc.).

Whether a field inducing signal constitutes a modulation signal(resulting in an electric field that may cause nerve modulation) or asub-modulation signal (resulting in an electric field not intended tocause nerve modulation) may ultimately be controlled by processor 144 ofexternal unit 120. For example, in certain situations, processor 144 maydetermine that nerve modulation is appropriate. Under these conditions,processor 144 may cause signal source 144 and amplifier 146 to generatea modulation control signal on primary antenna 150 (i.e., a signalhaving a magnitude and/or duration selected such that a resultingsecondary signal on secondary antenna 152 will provide a modulationsignal at implant electrodes 158 a and 158 b).

Processor 144 may be configured to limit an amount of energy transferredfrom external unit 120 to implant unit 110. For example, in someembodiments, implant unit 110 may be associated with a threshold energylimit that may take into account multiple factors associated with thepatient and/or the implant. For example, in some cases, certain nervesof a patient should receive no more than a predetermined maximum amountof energy to minimize the risk of damaging the nerves and/or surroundingtissue. Additionally, circuitry 180 of implant unit 110 may includecomponents having a maximum operating voltage or power level that maycontribute to a practical threshold energy limit of implant unit 110.Processor 144 may be configured to account for such limitations whensetting the magnitude and/or duration of a primary signal to be appliedto primary antenna 150.

In addition to determining an upper limit of power that may be deliveredto implant unit 110, processor 144 may also determine a lower powerthreshold based, at least in part, on an efficacy of the deliveredpower. The lower power threshold may be computed based on a minimumamount of power that enables nerve modulation (e.g., signals havingpower levels above the lower power threshold may constitute modulationsignals while signals having power levels below the lower powerthreshold may constitute sub-modulation signals).

A lower power threshold may also be measured or provided in alternativeways. For example, appropriate circuitry or sensors in the implant unit110 may measure a lower power threshold. A lower power threshold may becomputed or sensed by an additional external device, and subsequentlyprogrammed into processor 144, or programmed into implant unit 110.Alternatively, implant unit 110 may be constructed with circuitry 180specifically chosen to generate signals at the electrodes of at leastthe lower power threshold. In still another embodiment, an antenna ofexternal unit 120 may be adjusted to accommodate or produce a signalcorresponding to a specific lower power threshold. The lower powerthreshold may vary from patient to patient, and may take into accountmultiple factors, such as, for example, modulation characteristics of aparticular patient's nerve fibers, a distance between implant unit 110and external unit 120 after implantation, and the size and configurationof implant unit components (e.g., antenna and implant electrodes), etc.

Processor 144 may also be configured to cause application ofsub-modulation control signals to primary antenna 150. Suchsub-modulation control signals may include an amplitude and/or durationthat result in a sub-modulation signal at electrodes 158 a, 158 b. Whilesuch sub-modulation control signals may not result in nerve modulation,such sub-modulation control signals may enable feedback-based control ofthe nerve modulation system. That is, in some embodiments, processor 144may be configured to cause application of a sub-modulation controlsignal to primary antenna 150. This signal may induce a secondary signalon secondary antenna 152, which, in turn, induces a primary coupledsignal component on primary antenna 150.

To analyze the primary coupled signal component induced on primaryantenna 150, external unit 120 may include a feedback circuit 148 (e.g.,a signal analyzer or detector, etc.), which may be placed in direct orindirect communication with primary antenna 150 and processor 144.Sub-modulation control signals may be applied to primary antenna 150 atany desired periodicity. In some embodiments, the sub-modulation controlsignals may be applied to primary antenna 150 at a rate of one everyfive seconds (or longer). In other embodiments, the sub-modulationcontrol signals may be applied more frequently (e.g., once every twoseconds, once per second, once per millisecond, once per nanosecond, ormultiple times per second). Further, it should be noted that feedbackmay also be received upon application of modulation control signals toprimary antenna 150 (i.e., those that result in nerve modulation), assuch modulation control signals may also result in generation of aprimary coupled signal component on primary antenna 150.

The primary coupled signal component may be fed to processor 144 byfeedback circuit 148 and may be used as a basis for determining a degreeof coupling between primary antenna 150 and secondary antenna 152. Thedegree of coupling may enable determination of the efficacy of theenergy transfer between two antennas. Processor 144 may also use thedetermined degree of coupling in regulating delivery of power to implantunit 110.

Processor 144 may be configured with any suitable logic for determininghow to regulate power transfer to implant unit 110 based on thedetermined degree of coupling. For example, where the primary coupledsignal component indicates that a degree of coupling has changed from abaseline coupling level, processor 144 may determine that secondaryantenna 152 has moved with respect to primary antenna 150 (either incoaxial offset, lateral offset, or angular offset, or any combination).Such movement, for example, may be associated with a movement of theimplant unit 110, and the tissue that it is associated with based on itsimplant location. Thus, in such situations, processor 144 may determinethat modulation of a nerve in the patient's body is appropriate. Moreparticularly, in response to an indication of a change in coupling,processor 144, in some embodiments, may cause application of amodulation control signal to primary antenna 150 in order to generate amodulation signal at implant electrodes 158 a, 158 b, e.g., to causemodulation of a nerve of the patient.

In an embodiment for the treatment of OSA, movement of an implant unit110 may be associated with movement of the tongue, which may indicatethe onset of a sleep apnea event or a sleep apnea precursor. The onsetof a sleep apnea event of sleep apnea precursor may require thestimulation of the genioglossus muscle of the patient to relieve oravert the event. Such stimulation may result in contraction of themuscle and movement of the patient's tongue away from the patient'sairway.

In embodiments for the treatment of head pain, including migraines,processor 144 may be configured to generate a modulation control signalbased on a signal from a user, for example, or a detected level ofneural activity in a sensory neuron (e.g. the greater occipital nerve ortrigeminal nerve) associated with head pain. A modulation control signalgenerated by the processor and applied to the primary antenna 150 maygenerate a modulation signal at implant electrodes 158 a, 158 b, e.g.,to cause inhibition or blocking of a sensory nerve of the patient. Suchinhibition or blocking may decrease or eliminate the sensation of painfor the patient.

In embodiments for the treatment of hypertension, processor 144 may beconfigured to generate a modulation control signal based on, forexample, pre-programmed instructions and/or signals from an implantindicative of blood pressure. A modulation control signal generated bythe processor and applied to the primary antenna 150 may generate amodulation signal at implant electrodes 158 a, 158 b, e.g., to causeeither inhibition or stimulation of nerve of a patient, depending on therequirements. For example, a neuromodulator placed in a carotid arteryor jugular artery (i.e. in the vicinity of a carotid baroreceptor), mayreceive a modulation control signal tailored to induce a stimulationsignal at the electrodes, thereby causing the glossopharyngeal nerveassociated with the carotid baroreceptors to fire at an increased ratein order to signal the brain to lower blood pressure. Similar modulationof the glossopharyngeal nerve may be achieved with a neuromodulatorimplanted in a subcutaneous location in a patient's neck or behind apatient's ear. A neuromodulator place in a renal artery may receive amodulation control signal tailored to cause an inhibiting or blockingsignal at the electrodes, thereby inhibiting a signal to raise bloodpressure carried from the renal nerves to the kidneys.

Modulation control signals may include stimulation control signals, andsub-modulation control signals may include sub-stimulation controlsignals. Stimulation control signals may have any amplitude, pulseduration, or frequency combination that results in a stimulation signalat electrodes 158 a, 158 b. In some embodiments (e.g., at a frequency ofbetween about 6.5-13.6 MHz), stimulation control signals may include apulse duration of greater than about 50 microseconds and/or an amplitudeof approximately 0.5 amps, or between 0.1 amps and 1 amp, or between0.05 amps and 3 amps. Sub-stimulation control signals may have a pulseduration less than about 500, or less than about 200 nanoseconds and/oran amplitude less than about 1 amp, 0.5 amps, 0.1 amps, 0.05 amps, or0.01 amps. Of course, these values are meant to provide a generalreference only, as various combinations of values higher than or lowerthan the exemplary guidelines provided may or may not result in nervestimulation.

In some embodiments, stimulation control signals may include a pulsetrain, wherein each pulse includes a plurality of sub-pulses. Analternating current signal (e.g., at a frequency of between about6.5-13.6 MHz) may be used to generate the pulse train, as follows. Asub-pulse may have a duration of between 50-250 microseconds, or aduration of between 1 microsecond and 2 milliseconds, during which analternating current signal is turned on. For example, a 200 microsecondsub-pulse of a 10 MHz alternating current signal will includeapproximately 2000 periods. Each pulse may, in turn, have a duration ofbetween 100 and 500 milliseconds, during which sub-pulses occur at afrequency of between 25 and 100 Hz. For example, a 200 millisecond pulseof 50 Hz sub-pulses will include approximately 10 sub-pulses. Finally,in a pulse train, each pulse may be separated from the next by aduration of between 0.2 and 2 seconds. For example, in a pulse train of200 millisecond pulses, each separated by 1.3 seconds from the next, anew pulse will occur every 1.5 seconds. A pulse train of this embodimentmay be utilized, for example, to provide ongoing stimulation during atreatment session. In the context of OSA, a treatment session may be aperiod of time during which a subject is asleep and in need of treatmentto prevent OSA. Such a treatment session may last anywhere from aboutthree to ten hours. In the context of other conditions to which neuralmodulators of the present disclosure are applied, a treatment sessionmay be of varying length according to the duration of the treatedcondition.

Processor 144 may be configured to determine a degree of couplingbetween primary antenna 150 and secondary antenna 152 by monitoring oneor more aspects of the primary coupled signal component received throughfeedback circuit 148. In some embodiments, processor 144 may determine adegree of coupling between primary antenna 150 and secondary antenna 152by monitoring a voltage level associated with the primary coupled signalcomponent, a current level, or any other attribute that may depend onthe degree of coupling between primary antenna 150 and secondary antenna152. For example, in response to periodic sub-modulation signals appliedto primary antenna 150, processor 144 may determine a baseline voltagelevel or current level associated with the primary coupled signalcomponent. This baseline voltage level, for example, may be associatedwith a range of movement of the patient's tongue when a sleep apneaevent or its precursor is not occurring, e.g. during normal breathing.As the patient's tongue moves toward a position associated with a sleepapnea event or its precursor, the coaxial, lateral, or angular offsetbetween primary antenna 150 and secondary antenna 152 may change. As aresult, the degree of coupling between primary antenna 150 and secondaryantenna 152 may change, and the voltage level or current level of theprimary coupled signal component on primary antenna 150 may also change.Processor 144 may be configured to recognize a sleep apnea event or itsprecursor when a voltage level, current level, or other electricalcharacteristic associated with the primary coupled signal componentchanges by a predetermined amount or reaches a predetermined absolutevalue.

FIG. 7 provides a graph that illustrates this principle in more detail.For a two-coil system where one coil receives a radio frequency (RF)drive signal, graph 200 plots a rate of change in induced current in thereceiving coil as a function of coaxial distance between the coils. Forvarious coil diameters and initial displacements, graph 200 illustratesthe sensitivity of the induced current to further displacement betweenthe coils, moving them either closer together or further apart. It alsoindicates that, overall, the induced current in the secondary coil willdecrease as the secondary coil is moved away from the primary, drivecoil, i.e. the rate of change of induced current, in mA/mm, isconsistently negative. The sensitivity of the induced current to furtherdisplacement between the coils varies with distance. For example, at aseparation distance of 10 mm, the rate of change in current as afunction of additional displacement in a 14 mm coil is approximately −6mA/mm. If the displacement of the coils is approximately 22 mm, the rateof change in the induced current in response to additional displacementis approximately −11 mA/mm, which corresponds to a local maximum in therate of change of the induced current. Increasing the separationdistance beyond 22 mm continues to result in a decline in the inducedcurrent in the secondary coil, but the rate of change decreases. Forexample, at a separation distance of about 30 mm, the 14 mm coilexperiences a rate of change in the induced current in response toadditional displacement of about −8 mA/mm. With this type ofinformation, processor 144 may be able to determine a particular degreeof coupling between primary antenna 150 and secondary antenna 152, atany given time, by observing the magnitude and/or rate of change in themagnitude of the current associated with the primary coupled signalcomponent on primary antenna 150.

Processor 144 may be configured to determine a degree of couplingbetween primary antenna 150 and secondary antenna 152 by monitoringother aspects of the primary coupled signal component. For example, insome embodiments, the non-linear behavior of circuitry 180 in implantunit 110 may be monitored to determine a degree of coupling. Forexample, the presence, absence, magnitude, reduction and/or onset ofharmonic components in the primary coupled signal component on primaryantenna 150 may reflect the behavior of circuitry 180 in response tovarious control signals (either sub-modulation or modulation controlsignals) and, therefore, may be used to determine a degree of couplingbetween primary antenna 150 and secondary antenna 152.

As shown in FIG. 6, circuitry 180 in implant unit 110 may constitute anon-linear circuit due, for example, to the presence of non-linearcircuit components, such as diode 156. Such non-linear circuitcomponents may induce non-linear voltage responses under certainoperation conditions. Non-linear operation conditions may be inducedwhen the voltage potential across diode 156 exceeds the activationthreshold for diode 156. Thus, when implant circuitry 180 is excited ata particular frequency, this circuit may oscillate at multiplefrequencies. Spectrum analysis of the secondary signal on secondaryantenna 152, therefore, may reveal one or more oscillations, calledharmonics, that appear at certain multiples of the excitation frequency.Through coupling of primary antenna 150 and secondary antenna 152, anyharmonics produced by implant circuitry 180 and appearing on secondaryantenna 152 may also appear in the primary coupled signal componentpresent on primary antenna 150.

In certain embodiments, circuitry 180 may include additional circuitcomponents that alter the characteristics of the harmonics generated incircuitry 180 above a certain transition point. Monitoring how thesenon-linear harmonics behave above and below the transition point mayenable a determination of a degree of coupling between primary antenna150 and secondary antenna 152. For example, as shown in FIG. 6,circuitry 180 may include a harmonics modifier circuit 154, which mayinclude any electrical components that non-linearly alter the harmonicsgenerated in circuitry 180. In some embodiments, harmonics modifiercircuit 154 may include a pair of Zener diodes. Below a certain voltagelevel, these Zener diodes remain forward biased such that no currentwill flow through either diode. Above the breakdown voltage of the Zenerdiodes, however, these devices become conductive in the reversed biaseddirection and will allow current to flow through harmonics modifiercircuit 154. Once the Zener diodes become conductive, they begin toaffect the oscillatory behavior of circuitry 180, and, as a result,certain harmonic oscillation frequencies may be affected (e.g., reducedin magnitude).

FIGS. 8 and 9 illustrate this effect. For example, FIG. 8 illustrates agraph 300 a that shows the oscillatory behavior of circuitry 180 atseveral amplitudes ranging from about 10 nanoamps to about 20 microamps.As shown, the primary excitation frequency occurs at about 6.7 MHz andharmonics appear both at even and odd multiples of the primaryexcitation frequency. For example, even multiples appear at twice theexcitation frequency (peak 302 a), four times the excitation frequency(peak 304 a) and six times the excitation frequency (peak 306 a). As theamplitude of the excitation signal rises between 10 nanoamps and 40microamps, the amplitude of peaks 302 a, 304 a, and 306 a all increase.

FIG. 9 illustrates the effect on the even harmonic response of circuitry180 caused by harmonics modifier circuit 154. FIG. 9 illustrates a graph300 b that shows the oscillatory behavior of circuitry 180 at severalamplitudes ranging from about 30 microamps to about 100 microamps. As inFIG. 8, FIG. 9 shows a primary excitation frequency at about 6.7 MHz andsecond, fourth, and sixth order harmonics (peaks 302 b, 304 b, and 306b, respectively) appearing at even multiples of the excitationfrequency. As the amplitude of the excitation signal rises, however,between about 30 microamps to about 100 microamps, the amplitudes ofpeaks 302 b, 304 b, and 306 b do not continuously increase. Rather, theamplitude of the second order harmonics decreases rapidly above acertain transition level (e.g., about 80 microamps in FIG. 8). Thistransition level corresponds to the level at which the Zener diodesbecome conductive in the reverse biased direction and begin to affectthe oscillatory behavior of circuitry 180.

Monitoring the level at which this transition occurs may enable adetermination of a degree of coupling between primary antenna 150 andsecondary antenna 152. For example, in some embodiments, a patient mayattach external unit 120 over an area of the skin under which implantunit 110 resides. Processor 144 can proceed to cause a series ofsub-modulation control signals to be applied to primary antenna 150,which in turn cause secondary signals on secondary antenna 152. Thesesub-modulation control signals may progress over a sweep or scan ofvarious signal amplitude levels. By monitoring the resulting primarycoupled signal component on primary antenna 150 (generated throughcoupling with the secondary signal on secondary antenna 152), processor144 can determine the amplitude of primary signal (whether asub-modulation control signal or other signal) that results in asecondary signal of sufficient magnitude to activate harmonics modifiercircuit 154. That is, processor 144 can monitor the amplitude of thesecond, fourth, or sixth order harmonics and determine the amplitude ofthe primary signal at which the amplitude of any of the even harmonicsdrops. FIGS. 8 and 9 illustrate the principles of detecting couplingthrough the measurement of non-linear harmonics. These Figuresillustrate data based around a 6.7 MHz excitation frequency. Theseprinciples, however, are not limited to the 6.7 MHz excitation frequencyillustrated, and may be used with a primary signal of any suitablefrequency.

In some embodiments, the determined amplitude of the primary signalcorresponding to the transition level of the Zener diodes (which may bereferred to as a primary signal transition amplitude) may establish abaseline range when the patient attaches external unit 120 to the skin.Presumably, while the patient is awake, the tongue is not blocking thepatient's airway and moves with the patients breathing in a naturalrange, where coupling between primary antenna 150 and secondary antenna152 may be within a baseline range. A baseline coupling range mayencompass a maximum coupling between primary antenna 150 and secondaryantenna 152. A baseline coupling range may also encompass a range thatdoes not include a maximum coupling level between primary antenna 150and secondary antenna 152. Thus, the initially determined primary signaltransition amplitude may be fairly representative of a non-sleep apneacondition and may be used by processor 144 as a baseline in determininga degree of coupling between primary antenna 150 and secondary antenna152. Optionally, processor 144 may also be configured to monitor theprimary signal transition amplitude over a series of scans and selectthe minimum value as a baseline, as the minimum value may correspond toa condition of maximum coupling between primary antenna 150 andsecondary antenna 152 during normal breathing conditions.

As the patient wears external unit 120, processor 144 may periodicallyscan over a range of primary signal amplitudes to determine a currentvalue of the primary signal transition amplitude. In some embodiments,the range of amplitudes that processor 144 selects for the scan may bebased on (e.g., near) the level of the baseline primary signaltransition amplitude. If a periodic scan results in determination of aprimary signal transition amplitude different from the baseline primarysignal transition amplitude, processor 144 may determine that there hasbeen a change from the baseline initial conditions. For example, in someembodiments, an increase in the primary signal transition amplitude overthe baseline value may indicate that there has been a reduction in thedegree of coupling between primary antenna 150 and secondary antenna 152(e.g., because the implant has moved or an internal state of the implanthas changed).

In addition to determining whether a change in the degree of couplinghas occurred, processor 144 may also be configured to determine aspecific degree of coupling based on an observed primary signaltransition amplitude. For example, in some embodiments, processor 144may have access to a lookup table or a memory storing data thatcorrelates various primary signal transition amplitudes with distances(or any other quantity indicative of a degree of coupling) betweenprimary antenna 150 and secondary antenna 152. In other embodiments,processor 144 may be configured to calculate a degree of coupling basedon performance characteristics of known circuit components.

By periodically determining a degree of coupling value, processor 144may be configured to determine, in situ, appropriate parameter valuesfor the modulation control signal that will ultimately result in nervemodulation. For example, by determining the degree of coupling betweenprimary antenna 150 and secondary antenna 152, processor 144 may beconfigured to select characteristics of the modulation control signal(e.g., amplitude, pulse duration, frequency, etc.) that may provide amodulation signal at electrodes 158 a, 158 b in proportion to orotherwise related to the determined degree of coupling. In someembodiments, processor 144 may access a lookup table or other datastored in a memory correlating modulation control signal parametervalues with degree of coupling. In this way, processor 144 may adjustthe applied modulation control signal in response to an observed degreeof coupling.

Additionally or alternatively, processor 144 may be configured todetermine the degree of coupling between primary antenna 150 andsecondary antenna 152 during modulation. The tongue, or other structureon or near which the implant is located, and thus implant unit 110, maymove as a result of modulation. Thus, the degree of coupling may changeduring modulation. Processor 144 may be configured to determine thedegree of coupling as it changes during modulation, in order todynamically adjust characteristics of the modulation control signalaccording to the changing degree of coupling. This adjustment may permitprocessor 144 to cause implant unit 110 to provide an appropriatemodulation signal at electrodes 158 a, 158 b throughout a modulationevent. For example, processor 144 may alter the primary signal inaccordance with the changing degree of coupling in order to maintain aconstant modulation signal, or to cause the modulation signal to bereduced in a controlled manner according to patient needs.

More particularly, the response of processor 144 may be correlated tothe determined degree of coupling. In situations where processor 144determines that the degree of coupling between primary antenna 150 andsecondary antenna has fallen only slightly below a predeterminedcoupling threshold (e.g, during snoring or during a small vibration ofthe tongue or other sleep apnea event precursor), processor 144 maydetermine that only a small response is necessary. Thus, processor 144may select modulation control signal parameters that will result in arelatively small response (e.g., a short stimulation of a nerve, smallmuscle contraction, etc.). Where, however, processor 144 determines thatthe degree of coupling has fallen substantially below the predeterminedcoupling threshold (e.g., where the tongue has moved enough to cause asleep apnea event), processor 144 may determine that a larger responseis required. As a result, processor 144 may select modulation controlsignal parameters that will result in a larger response. In someembodiments, only enough power may be transmitted to implant unit 110 tocause the desired level of response. In other words, processor 144 maybe configured to cause a metered response based on the determined degreeof coupling between primary antenna 150 and secondary antenna 152. Asthe determined degree of coupling decreases, processor 144 may causetransfer of power in increasing amounts. Such an approach may preservebattery life in the external unit 120, may protect circuitry 170 andcircuitry 180, may increase effectiveness in addressing the type ofdetected condition (e.g., sleep apnea, snoring, tongue movement, etc.),and may be more comfortable for the patient.

In some embodiments, processor 144 may employ an iterative process inorder to select modulation control signal parameters that result in adesired response level. For example, upon determining that a modulationcontrol signal should be generated, processor 144 may cause generationof an initial modulation control signal based on a set of predeterminedparameter values. If feedback from feedback circuit 148 indicates that anerve has been modulated (e.g, if an increase in a degree of coupling isobserved), then processor 144 may return to a monitoring mode by issuingsub-modulation control signals. If, on the other hand, the feedbacksuggests that the intended nerve modulation did not occur as a result ofthe intended modulation control signal or that modulation of the nerveoccurred but only partially provided the desired result (e.g, movementof the tongue only partially away from the airway), processor 144 maychange one or more parameter values associated with the modulationcontrol signal (e.g., the amplitude, pulse duration, etc.).

Where no nerve modulation occurred, processor 144 may increase one ormore parameters of the modulation control signal periodically until thefeedback indicates that nerve modulation has occurred. Where nervemodulation occurred, but did not produce the desired result, processor144 may re-evaluate the degree of coupling between primary antenna 150and secondary antenna 152 and select new parameters for the modulationcontrol signal targeted toward achieving a desired result. For example,where stimulation of a nerve causes the tongue to move only partiallyaway from the patient's airway, additional stimulation may be desired.Because the tongue has moved away from the airway, however, implant unit110 may be closer to external unit 120 and, therefore, the degree ofcoupling may have increased. As a result, to move the tongue a remainingdistance to a desired location may require transfer to implant unit 110of a smaller amount of power than what was supplied prior to the laststimulation-induced movement of the tongue. Thus, based on a newlydetermined degree of coupling, processor 144 can select new parametersfor the stimulation control signal aimed at moving the tongue theremaining distance to the desired location.

In one mode of operation, processor 144 may be configured to sweep overa range of parameter values until nerve modulation is achieved. Forexample, in circumstances where an applied sub-modulation control signalresults in feedback indicating that nerve modulation is appropriate,processor 144 may use the last applied sub-modulation control signal asa starting point for generation of the modulation control signal. Theamplitude and/or pulse duration (or other parameters) associated withthe signal applied to primary antenna 150 may be iteratively increasedby predetermined amounts and at a predetermined rate until the feedbackindicates that nerve modulation has occurred.

Processor 144 may be configured to determine or derive variousphysiologic data based on the determined degree of coupling betweenprimary antenna 150 and secondary antenna 152. For example, in someembodiments the degree of coupling may indicate a distance betweenexternal unit 120 and implant unit 110, which processor 144 may use todetermine a position of external unit 120 or a relative position of apatient's tongue. Monitoring the degree of coupling can also providesuch physiologic data as whether a patient's tongue is moving orvibrating (e.g, whether the patient is snoring), by how much the tongueis moving or vibrating, the direction of motion of the tongue, the rateof motion of the tongue, etc.

In response to any of these determined physiologic data, processor 144may regulate delivery of power to implant unit 110 based on thedetermined physiologic data. For example, processor 144 may selectparameters for a particular modulation control signal or series ofmodulation control signals for addressing a specific condition relatingto the determined physiologic data. If the physiologic data indicatesthat the tongue is vibrating, for example, processor 144 may determinethat a sleep apnea event is likely to occur and may issue a response bydelivering power to implant unit 110 in an amount selected to addressthe particular situation. If the tongue is in a position blocking thepatient's airway (or partially blocking a patient's airway), but thephysiologic data indicates that the tongue is moving away from theairway, processor 144 may opt to not deliver power and wait to determineif the tongue clears on its own. Alternatively, processor 144 maydeliver a small amount of power to implant unit 110 (e.g., especiallywhere a determined rate of movement indicates that the tongue is movingslowly away from the patient's airway) to encourage the tongue tocontinue moving away from the patient's airway or to speed itsprogression away from the airway. The scenarios described are exemplaryonly. Processor 144 may be configured with software and/or logicenabling it to address a variety of different physiologic scenarios withparticularity. In each case, processor 144 may be configured to use thephysiologic data to determine an amount of power to be delivered toimplant unit 110 in order to modulate nerves associated with the tonguewith the appropriate amount of energy.

The disclosed embodiments may be used in conjunction with a method forregulating delivery of power to an implant unit. The method may includedetermining a degree of coupling between primary antenna 150 associatedwith external unit 120 and secondary antenna 152 associated with implantunit 110, implanted in the body of a patient. Determining the degree ofcoupling may be accomplished by processor 144 located external toimplant unit 110 and that may be associated with external unit 120.Processor 144 may be configured to regulate delivery of power from theexternal unit to the implant unit based on the determined degree ofcoupling.

As previously discussed, the degree of coupling determination may enablethe processor to further determine a location of the implant unit. Themotion of the implant unit may correspond to motion of the body partwhere the implant unit may be attached. This may be consideredphysiologic data received by the processor. The processor may,accordingly, be configured to regulate delivery of power from the powersource to the implant unit based on the physiologic data. In alternativeembodiments, the degree of coupling determination may enable theprocessor to determine information pertaining to a condition of theimplant unit. Such a condition may include location as well asinformation pertaining to an internal state of the implant unit. Theprocessor may, according to the condition of the implant unit, beconfigured to regulate delivery of power from the power source to theimplant unit based on the condition data.

Other embodiments of the present disclosure will be apparent to thoseskilled in the art from consideration of the specification and practiceof the present disclosure.

What is claimed is:
 1. An implant unit, comprising: a substrate; animplantable circuit arranged on the substrate; and an encapsulationstructure disposed over at least a portion of the substrate and at leasta portion of the implantable circuit, the encapsulation structureincluding: a first polymer layer having a first density; a secondpolymer layer disposed over the first polymer layer and having a densitywhich is less than the first density; and at least one pair ofmodulation electrodes connected to the implantable circuit, wherein thefirst polymer layer includes a first window of exposure over one or moreof the modulation electrodes, the first window of exposure having afirst area; and wherein the second polymer layer includes a secondwindow of exposure over one or more of the modulation electrodes and atleast partially extending over the first window of exposure, the secondwindow of exposure having a second area that is larger than the firstarea of the first window of exposure.
 2. The implant unit of claim 1,wherein the first polymer layer includes parylene and the second polymerlayer includes silicone.
 3. The implant unit of claim 2, wherein theparylene includes parylene C.
 4. The implant unit of claim 1, whereinthe substrate comprises a flexible carrier.
 5. The implant unit of claim1, further comprising an antenna encapsulated by the first polymer layerand the second polymer layer.
 6. The implant unit of claim 1, whereinthe implantable circuit includes at least one meandering electricaltrace configured to maintain electrical contact during flexing of thedevice.
 7. The implant unit of claim 1, wherein the substrate includesat least one perforation, and wherein the second polymer layer isdisposed on a first side of the substrate, on a second side of thesubstrate opposite to the first side, and through the at least oneperforation.
 8. The implant unit of claim 1, further comprising at leastone suture hole through the substrate and the second polymer layer and asurgical mesh disposed within the at least one suture hole, wherein thesurgical mesh is encapsulated by the second polymer layer.
 9. Theimplant unit of claim 1, further comprising at least one suture holethrough the substrate and the second polymer layer.
 10. The implant unitof claim 1, wherein the device has a thickness of less than 4 mm. 11.The implant unit of claim 1, wherein the first polymer layer isdeposited by chemical vapor deposition.
 12. The implant unit of claim 1,wherein a thickness of the first polymer layer is between 10 microns and80 microns thick.
 13. The implant unit of claim 1, wherein the substrateincludes a flexible carrier.
 14. The implant unit of claim 13, whereinthe flexible carrier has a thickness of less than about 4 mm.
 15. Theimplant unit of claim 13, wherein the flexible carrier includes at leastone of silicone, polyimides, phenyltrimethoxysilane, polymethylmethacrylate, Parylene C, polyimide, liquid polyimide, laminatedpolyimide, black epoxy, polyether ether ketone, Liquid Crystal Polymer,or Kapton.
 16. The implant unit of claim 1, further including a thirdpolymer layer disposed over the second polymer layer, wherein the thirdpolymer layer has a density less than the second polymer layer.
 17. Theimplant unit of claim 1, wherein the third polymer layer includesparylene.